atoi: fix leading zeros in string to int conversion

vlib/builtin/string_int_test.v

@@ -1,9 +1,25 @@
 fn test_common_atoi() {
+	// test common cases
 	assert "70zzz".int() == 70
 	assert "2901issue".int() == 2901
 	assert '234232w'.int() == 234232
 	assert '-9009x'.int() == -9009
 	assert '0y'.int() == 0
+	
+	// test lead zeros
+	assert '0000012'.int() == 12
+	assert '-0000012'.int() == -12
+	assert '0x001F'.int() == 31
+	assert '-0x001F'.int() == -31
+	assert '0x001f'.int() == 31
+	assert '0o00011'.int() == 9
+	assert '0b00001001'.int() == 9
+
+	// test underscore in string
+	assert '-10_000'.int() == -10000
+	assert '-0x00_0_f_ff'.int() == -0xfff
+	assert '10_000_000'.int() == 10000000
+
 	for n in -10000 .. 100000 {
 		s := n.str()+"z"
 		assert s.int() == n

vlib/strconv/atoi.v

@@ -50,6 +50,11 @@ pub fn common_parse_uint(s string, _base int, _bit_size int, error_on_non_digit
 				base = 16
 				start_index += 2
 			}
+			// manage leading zeros in decimal base's numbers
+			else if s.len >=2 && ( s[1] >=  `0` && s[1] <= `9`) {
+				base = 10 
+				start_index ++
+			}
 			else {
 				base = 8
 				start_index++